Environment: `Browser`, `Node.js`.<br/>
[Ext Glob](https://github.com/micromatch/micromatch#extglobs): `/**/*.page.*([a-zA-Z0-9])`.

A `.page.js` file can export the following:
- `export { Page }` (or `export default`)
- `export { onBeforeRender }`
- Custom exports (which are available at `pageContext.pageExports`)

The `.page.js` file is isomorphic: it can run in the browser as well as in Node.js.

The `.page.js` file is lazy-loaded: it is loaded only when needed which means that if no URL request were to match the page's route then `.page.js` is never loaded in the browser nor in the Node.js process' memory.
